Scorched Earth
by sporadicallyceaseless
Summary: New York has a serial arsonist. The 11th precinct has a case. And Joan Watson has a secret, a stalker, and a Sherlock.


_AN:_ _Set post-season 4, though that's fairly unimportant._ _Spoilers for season 4, regarding Lin. Though she's not a main character and only pops up in the first chapter._

 **One:** The Floor Out From Under You

 _The doorframe shudders, rocked by the force of massive shoulders. Joan spares it half a glance, preoccupied with stemming the bleeding from the other woman's split lip._

" _Here," she says gently, offering a plush washcloth she nabbed off the edge of the nearby sink. "Apply pressure."_

 _Angela swipes her palms brusquely over her eyes, not completely clearing the tears from her face. She takes the washcloth but doesn't hold it to her lip._

 _She sucks in a long, shaky breath. "Joan...my husband…Joan, he's not a very nice man."_

 _The doorknob rattles hard in place and they both jump when they hear metal thunk against the marble tile as the doorknob gives from the outside and hits the floor._

 _Breathing heavily, Joan slides herself across the floor to examine the damage, then slumps in partial relief. "It's okay…the lock's intact. It's okay."_

 _But she firmly plants her back against the seam between the door and the wall for good measure._

 _Angela curls tighter into herself and presses her fists against her ears, her shoulders shaking._

 _Over the pounding and the screaming and the threats, Joan hears something that, until now, she's only heard from ER patients that hadn't come in alone but left that way- a gutted, high wail that escapes when a person is caught between pain and grief and confusion and doesn't see a way out._

 _So Joan offers one._

* * *

"This isn't what I meant when I told you to get this stuff out of the bathroom," Joan sighs. "And I think you knew that when you did…all this."

She gestures vaguely at the nylon covered media room and rests her shoulder against the doorframe. An impatient pointer finger struggles to find the opening in the fabric, then emerges, triumphant.

 _Just a moment._

Rolling her eyes, Joan obliges and waits.

The door panel is thrown to the side, and her partner appears in a plume of steam, goggles fogged and hair plastered wetly to his forehead. The makeshift parachute hothouse teeters precariously as he tries to extricate himself from the mess.

Joan frowns. "You smell like a musty gym sock."

Sherlock nods, rocking on the balls of his feet. "An unfortunate byproduct of the collaboration between _that_ 55-gallon drum of swamp water and my own perspiration."

"Lovely," Joan grimaces. "Does that mean what was in the bathtub earlier was…you know what, never mind. The captain called."

Having said the magic words, Joan retreats from swamp, hoping she hadn't been there long enough for the smell to retreat with her. The hall is humid, overflow from the media room, and Watson pauses to smooth a new spot of peeling wallpaper back into place.

The brownstone could probably stand a little work- especially if Sherlock succeeds in rotting the floor out from under himself with that artificial swamp.

"Watson!"

It's hard to hear over the sound of the shower she's grateful he's taking, but it sounds like he's asking for a briefing on the information she has so far.

"Housefire!" she calls up the stairs from the landing. "One dead. Suspicious circumstances."

"Housefires increase by tenfold in the winter months! How are we to know this isn't a case of improper use of a _space heater_?"

"I'd imagine they increase by twelvefold when you marinate the place in accelerant!"

Sooner than should be possible, Sherlock is thumping down the stairs, yanking a winter hat over his damp hair.

"I'll accompany you to the initial consultation, but I'm afraid if it amounts to anything, I'll have to duck out early. The decomposition I'm attempting to replicate is time sensitive, and my _paleosuchus palpebrosus_ can only be left unsupervised for a finite time frame."

Joan ignores that, not loving the sound of the prefix ' _paleo-_ 'but refusing to ask.

"Is the implication of that sentence that there's a decomposing pig in the brownstone?" she asks redundantly, having surmised the answer before bothering to ask.

"You needn't be alarmed, Watson," Sherlock says brightly. "I'm adept in the art of crime scene cleanup. Though I doubt there will be much to attend to after the dwarf caim-"

"Stop," Watson orders sharply. "Don't turn me into someone who knows what's up there. It makes me feel complacent."

She turns on her heel and lets the door close behind her. It'll take Sherlock at least another minute to finagle himself into his boots and gloves.

Besides, in her experience, it's easier to hail a cabby herself.

* * *

They should undoubtedly not be in the building. They don't need to be. It's already been well documented by the fire marshals, who've come to and made available their own conclusions. It's structurally unsound and probably does not technically fit the definition of a building anymore.

So, of course, they're on the second floor.

Sherlock holds out a hand to help her steady herself as she steps over the charred remains of what looks like a bathtub.

"So the medical examiner said she was found over there, in the corner," Joan sighs. She rubs her hands briskly over her arms, glancing mournfully up at the hole in the roof that's letting the winter air in. A flash of something catches her eye and she crouches down to examine a pile of flat, geometric debris. Her gloved thumb smoothes the soot away to reveal a glimpse of her own face.

"There was a mirror here. A vanity, maybe. Looks like she was getting ready for bed when the fire reached the bathroom."

"So she was quite literally cornered," Sherlock murmurs. "Where would you place the odds of our perpetrator just _happening upon_ his target where she could be most easily corralled?"

"Low, but it's not impossible," Joan admits. "He could have had a weapon- chased her until she panicked and accidentally cornered herself."

Shaking his head, her partner lightly scrambles over the obstacles in his path to get the coroner's report left on the ash-contaminated, but surviving countertop. As he flips through the pages, furiously trying to get at whatever he's after, Joan carefully chooses the most stable looking floorboards to step on to join him.

"Acetone…" Sherlock mumbles, mostly to himself. "The accelerant used was acetone. The fire marshal posited that it may have been utilized out of opportunity. Snatched up in the heat of the moment."

Watson shakes her head. "No woman keeps enough nail polish remover in her bathroom to do this. So he brought it on his own. But that doesn't make any sense. Gasoline would have been just as easy, if not easier, to obtain in bulk and twenty times cheaper."

"Though ever so slightly less flammable…tell me Watson, if you were to smell gasoline in your home, what would your immediate response be?"

"Evacuate," she says absently. There's a spot of silver on the floor, and for a second she thinks it's a knife, but when she prods it gently, it turns out to be what looks like the shrunken, broken handle of what looks like a hairbrush. "Or at the very least go looking for where it's coming from."

"And if you were to detect the strong odor of _acetone_?"

"I'd think I'd spilled it somewhere." Joan nods and sighs. "Especially in the bathroom. So he was in the house, about to torch it, but he didn't want her to know it until it was too late."

Despite herself, Joan continues to eye the hairbrush, something prickling at the back of her mind. But Sherlock's doing that thing where he _doesn't profile_ , because that would make him no better than the _storytellers_ at the FBI field office that he loathes so completely, but _does_ postulate on the nature of a man that puts his victims through the ordeal of being trapped in a housefire whilst awake and aware of their own impending demise; so she doesn't dwell on it.

"She was on the second floor," Watson says instead. "There was no way out. Why go to the trouble of starting the fire up here? Why not start it on the stairs and get out easy?"

She looks up to see him standing on a charred wastebasket, holding the file folder aloft to get a side-by-side comparison of something. Probably, he's not listening to her, and she's just come to terms with that when starts talking again and proves her wrong.

"Either our perpetrator wasn't as skilled an arsonist as you, Watson, or he had the intense desire to watch his victim _squirm_."

They both glance out the door at the path of destruction the fire left in its wake. "And it appears he went to great lengths to make that happen."

Watson nods, distracted by the ringing coming from her jacket pocket.

"It's Lin. She's in the ER. She says she was mugged."

"Go," Sherlock says immediately. "I'll manage everything here. You'll call if you need assistance, of course. We'll discuss this further when we meet again, at the brownstone."

She nods, trying to mentally trace the safest route out of the bathroom.

"Or in the hospital," Watson sighs. "When you fall through this floor and break every bone in your body."

* * *

Lin is the loudest person in a room full of people much worse off than she is, and the fact that Watson can follow the sound of her exasperated complaints from the ER entrance to her curtained off gurney makes her the slightest bit grateful they didn't grow up together. There's a nurse taking her sister's blood pressure when she gets there, but from the looks of things, Lin's blood pressure is fine while the nurse's is going through the roof.

Watson relieves the nurse of her burden with the 'I'm sorry your patient is a pain in the ass' look she cultivated her first year of residency. The nurse pronounces Lin 'fine but on thin ice' with a clipped nod then leaves the sisters to themselves.

"You're alright?" Joan confirms softly, resting her hand on Lin's undamaged arm.

Smiling, Lin nods, slightly lifting her sling to show off the fancy new splint on her wrist. "Barely a scratch. I told the goons in the ambulance I didn't have to come here."

Joan winces and nods. "The paramedics were just doing their jobs."

Gently, she turns Lin's wrist in her hand, tracing her thumbs down the blue, foam splint to feel for irregularities. Once Lin passes her second exam, Joan releases her and steps into the present, clearing the cobwebs from her mind until she's more detective than doctor.

"You said they didn't get him?" Lin shakes her head. "I'll let a friend at the police station know what to be on the lookout for. And I promise, I'll do everything I can-"

"Wait, Joan, hold up," Lin scoffs. "That's not why I called you. I'm cool. I don't need anything from you."

There's the Lin she knows.

"The guy didn't even take my wallet. Joan, he was looking for you."

The look on Lin's face is a little gleeful- she's likely enjoying having more information than Joan for once- until Joan nudges her knee to remind her to turn it down a little.

Lin rolls her eyes. "Sorry. But he was. Tall guy, big arms." She demonstrates, holding her palm inches away from Joan's own bicep to highlight the difference. "Blonde, business suit kinda guy? Showed me a picture and everything. You had bangs in it, like straight across ones, and can I just say-?"

"No," Joan interrupts. "You can't."

None of that rings a bell or matches up with anything they're currently working on. Joan frowns.

"I'm so sorry, Lin. I had no idea. How-? How would someone even know you exist?"

Lin shrugs and hops down from the gurney. "One of us is a detective and it's not me. I work in real estate? And speaking of…"

She grabs the pen attached to her chart and motions for Joan's hand. Rolling her eyes, Joan removes her glove and stashes it in her pocket before she holds her palm out. Lin scrawls an address over her head and heart lines, wincing at the awkward feeling of writing with her nondominant hand. It's barely legible, hardly worth writing when she's going to have to text Lin to hear it again later.

"What is this?" she sighs.

"I gave him this address. Told him you wouldn't be home until tomorrow night. So you and Sherlock have time to set up a snatch or a sting or whatever it is you do."

"Smart," Joan nods. "Thank you. This is one of yours?"

Lin nods. "An add on. A junk listing that came bundled with a property I could actually move. It's yours for as long as you need it. I'm assuming you don't need a key?"

Smiling, Joan shakes her head then nods towards the entrance, silently asking if Lin wants to be sprung. She does, so she grabs her bag and coat and Joan helps her slip by the admitting nurse who's looking for her with a mound of paperwork on her clipboard.

It's the least she can do, after whatever she apparently got Lin into.

She happily yields the first cab to Lin, but catches her sleeve to get her to hold up.

"I really am sorry about this, Lin," she says sincerely. "I never wanted to put you in this situation."

Lin leans forward and for a second, it looks like she's going to hug her. But while they're sisters, they're not quite there yet, so she steps back again and nods instead.

"I know, and it's okay. Just be careful okay?"

"I will do everything in my power to keep you out of this, whatever it is."

Lin rolls her eyes, waving at the impatient cabby who got sick of her hanging half in, half out of his cab and honked his horn.

"Yeah, I was talking about you not getting yourself killed. But okay, make it about me."

* * *

Sherlock's cross-legged on the living room floor, having considerately placed himself on a tarp to keep the swamp water on his clothes from seeping into their floorboards. Of course, it would have been more considerate for him to just _shower_. Again.

"Watson," he nods. "I trust your sister is in good health?"

Watson nods as she undoes her coat. She's preoccupied and a little unnerved by what happened to Lin- so it takes her a second to realize he can't see her and answer out loud.

"I'm exceptionally glad to hear that. On the home front, I'm afraid I have more unfortunate news."

Joan stills, looping her scarf around the coat hook. "Are you alright?"

It must come out at little oddly because Sherlock stops what he's doing (whatever that is) and turns to face her.

"Yes, quite." He frowns. "My experiment didn't move in the direction I had hoped it would, but I'll persist, as I always do. You, on the other hand, seem on edge."

She could tell him. And she probably should. There's a possibility that this could come down on him in some way, though she doubts it. It seems counterproductive to look for her if you know where to find her roommate.

However, it could be nothing. And if it's not, there will be plenty of time to read him in later.

"I'm fine," Watson sighs. "At least I will be if you do your persisting elsewhere. I think that stuff is attracting mosquitos."


End file.
